1. Field
Embodiments of the present disclosure relate to a direct current (DC) motor, and more particularly, to a DC motor including a rotation detection unit.
2. Description of the Related Art
When a current is applied to a direct current (DC) motor, the resulting electromagnetic force generated by a magnetic circuit included in the DC motor causes a rotor to rotate. Terminals that contact brushes change in accordance with the rotation of the rotor, and the rotor continuously rotates because the current flowing in a rotor coil periodically changes direction. The rotation velocity of the rotor is proportional to the current flowing in the rotor coil. However, the rotation velocity may also change according to a rotation load. It is therefore difficult to control the velocity or position of the rotor accurately by using only the DC motor. In particular, in the case of a DC motor being applied to an autofocus (AF) lens or a zoom lens of a compact camera that requires accurate control, a rotation detection sensor unit for detecting the amount of rotation of the rotor shaft is necessary.
Thus, a rotation velocity, amount of rotation, or angle of rotation of the DC motor may be detected by using a rotation detection unit, and based on the detected rotation velocity, amount of rotation, or angle of rotation of the DC motor, a location or velocity of a lens may be controlled. An optical encoder using a photo-interrupter (PI) type sensor or a photo-reflector (PR) type sensor, or a magnetic encoder using a Hall sensor or a magnetoresistive (MR) sensor may be generally used to determine a rotation velocity, amount of rotation, or angle of rotation of the DC motor.
A torque generated by the motor may be transmitted to an object via a gear unit installed on an external surface of a main body of the motor, but a rotation detection unit for detecting a rotation amount of a rotor shaft may be necessary to control a rotation amount or velocity of the motor. When the rotation detection unit is installed in the gear unit, space in a lengthwise direction of the motor is required. However, this space may be hinder miniaturization of a product to which the DC motor is applied.